1. Field of the Invention
The present invention relates to nuclear reactor systems, and more particularly to frameworks in the form of grids which serve as supports, rests or suspensions for the fuel elements in water cooled nuclear reactors that are characterized by pressurized water or boiling water.
2. Description of the Prior Art
Fuel element supports usually are formed by a network of intersecting beams which rest with their two ends on a peripheral hoop. Each of these beams is a metal block, placed on edge, equal in length to its span, and the complete series of metal blocks constituting the grid is cut to length, suitably notched to allow them to interlock, then placed along the guidelines of the lattice and welded together at their interlocking points.
Such methods of construction are time-consuming, costly and laborious. They require the preparation and machining of each beam at the future points of mutual intersection with the beams in the grid, the assembly of all these beams to form the complete grid, and welding the beams together at the intersections. This welding is a particularly delicate operation that should be carried out according to a carefully established program to compensate, insofar as possible, for warping of the unit as a whole because of the welds at each of the individual points of intersection. This welding program, however, does not insure the desired precision for the location of the intersections in the lattice that finally is produced. As a consequence, framework attachment means, such as centering pins, threaded holes, and the like that are designed to receive reactor core components must be installed or formed after the framework has been assembled. Because the framework is heavy and bulky, machining and installation of these attachment means is a troublesome operation. The welds, moreover, that are deposited on the lines of intersection sometimes tend to be weak because of the "notch effect." These welds also are not very adaptable to automated non-destructive inspection and quality control methods.
It is an object of the present method to eliminate these drawbacks and to facilitate, in a general way, the construction of support grids of the above-mentioned type.